Electric power grids that carry electrical power to homes and businesses are sometimes prone to failure, resulting in a blackout for the affected areas. The causes for grid failure include imbalances between load and power generation.
Power grids are usually monitored constantly for alternating current (AC) frequency. Power grid operators try to keep the AC frequency as close to a fixed frequency as possible. For example, the nominal AC frequency of the power grid in the US is 60 Hz, while in Europe and parts of Japan, the nominal AC frequency of the power grid is 50 Hz. While the AC frequency is nominally set at a certain value, the actual AC frequency drifts around the nominal value as a result of load and generation effects. An AC frequency error of ±0.02 Hz is well within the bounds of normal operation. The drift of the AC frequency, or drift frequency, refers to the deviation of the AC frequency from the nominal value. Typically, the drift frequency does not exceed 0.05 Hz in a stable system. The monitoring of the AC frequency, however, usually does not reveal information that would indicate impending failure in the power grid until it is too late to take actions that could prevent the failure.
A basic component of power grid monitoring and detection systems are phase measurement units (PMUs). A collection of PMUs connected to the power grid bus at various points in the grid provide real-time measurements of the phase of the electrical power signals in the grid.
Since the formation of the Eastern Interconnection Phasor Project (EIPP) and the subsequent formation of the North American SynchroPhasor Initiative (NASPI), utility companies have recognized the value of real-time data from PMUs. For example, during storm events, the role of PMUs in detecting and maintaining a power island has saved companies millions of dollars. However, there is still a need for effective techniques for the measurement, communication, and analysis of PMU data to provide useful predictions of grid instability. Current PMU measurement and analysis methods, however, do not enable the needed techniques.